1. Field of the Invention
The present invention relates to a work conveying system for manufacturing a product including multiple parts, such as business equipment, through sequential working steps performed by multiple working apparatuses.
2. Description of the Related Art
In a conventional production line in which business equipment and the like are produced, a workpiece is sequentially conveyed to multiple holding bases placed at certain intervals along a row of working apparatuses, and the workpiece is positioned and held by each of the holding bases at a predetermined working position. Then, working robots or the like sequentially perform an assembly work or processing on the workpiece.
FIG. 10 illustrates a work conveying system according to a conventional example. In the conveying system, workpieces 112 are intermittently conveyed on a rail track 114, and works are performed by working apparatuses 118a, 118b, and 118c disposed at stop positions of the workpieces 112. On the rail track 114, there is provided a base table 115 that advances (in an arrow direction) and retreats along the rail track 114. Multiple jigs 120a to 120c are disposed at intervals of a distance P on the base table 115. Holding bases 121a to 121c are fixed and disposed at the stop positions of the workpieces 112. The respective working apparatuses 118a, 118b, and 118c perform the works on the workpieces 112 held by the respective holding bases 121a, 121b, and 121c. After completion of the works, the workpieces 112 are disposed on the respective jigs 120a, 120b, and 120c. The base table 115 moves (advances) in the arrow direction by the distance P along the rail track 114, and accordingly the respective jigs 120a, 120b, and 120c are conveyed for next working steps. The workpieces 112, which are conveyed together with the respective jigs 120a, 120b, and 120c, are held by the holding bases for the next working steps, and then the next works are started. During the works, the base table 115 moves (retreats) in a direction opposite to the arrow direction by the distance P along the rail track 114. Through repetition of the above-mentioned operations, the workpieces 112 are sequentially conveyed. This system is generally called a shuttle conveying system.
Further, Japanese Patent Application Laid-Open No. H06-156667 discloses the shuttle conveying apparatus including the means for sliding components disposed at different pitches. The shuttle conveying apparatus includes: the shuttle member reciprocating through a stroke of a certain distance; and the multiple base table portions disposed at the same intervals. According to a cycle of ascent, advance, descent, and retreat of the shuttle member, the transportation tables on the base table portions are progressed onto the adjacent base table portions, and in addition, the base table portions are slid. This enables conveyance onto the base table portions disposed at different pitches.
However, in a production line constituted by multiple working apparatuses, the respective working apparatuses, which perform assembly or processing individually, generally have different working time periods. Further, even if using the same working apparatuses, working methods are different depending on the kind of the workpiece, and hence the working time periods may be elongated or shortened. In addition, even if using the same working apparatuses and the same kind of the workpiece, the working time periods are generally different from each other depending on an individual difference of the workpiece, an individual difference of a part to be assembled, and a state of coating applied onto the workpiece. For example, in a case of fitting and mounting a gear to a shaft mounted to the workpiece while correcting an angle of the gear to a predetermined angle, the angle of the gear gripped by the working robot differs every time, and hence a time period to correct the angle of the gear with respect to the shaft differs every time. Accordingly, there are differences in working time period, and the working time periods become longest in the multiple working apparatuses in many cases. In this case, in the conventional shuttle conveying system for conveying the workpieces in unison, conveyance is performed through a wait for completion of the working step of assembling the gear.
In general, in the conventional system, such as the shuttle conveying system, for conveying the workpieces in unison, it is necessary to convey the workpieces in unison through a wait for completion of the work of the working apparatus having the longest working time period in one cycle. Thus, a sum of the longest working time period and a conveying time period corresponds to one cycle time period, and hence any one of or both of the time periods have needed to be increased in speed (be cut) for improvement of productivity.
Further, even in the conveying system disclosed in Japanese Patent Application Laid-Open No. H06-156667, the workpieces are conveyed in unison, and hence the sum of the working time period and the conveying time period corresponds to one cycle time period. Thus, in the case where there are differences in working time period in the multiple working apparatuses, in order to cut the one cycle time period, it is necessary to increase conveying speed of the conveying apparatus or to cut the working time periods of all the working apparatuses that work for a long period of time, and hence it is difficult to improve productivity. In addition, the conveying system has structure in which the base table portion for positioning the workpiece at the working position of each of the working apparatuses is fixed and placed separately from a conveying section, and hence the entire structure of the system is complex, which is disadvantageous for space saving.